In recent years, in a mobile body, for example, an electrical power train system of a car, to realize various functions such as engine start, booster acceleration, movement start, brake regeneration, and mobile device driving at the time of idle stop, a field wound-rotor type AC rotating electric machine has been used. As such an AC rotating electric machine, conventionally, for example, the one described in Japanese Patent Laid-open No. 2004-7964 is known.